Finding the Mother Tree: Uncovering the Wisdom and Intelligence of the Forest

by Suzanne Simard

The thicker the mantle and the greater the number of fungal threads the root could feed, the more extensively the mycelium could laminate the soil minerals, and the more nutrients it could acquire from the grains and transport back to the root in trade. Root begets fungus begets root begets fungus. The partners keeping a positive feedback loop until a tree is made and a cubic foot of soil is packed with a hundred miles of mycelium. A web of life like our own cardiovascular system of arteries, veins, and capillaries.

These young trees got their start in the shadow of the old by linking into their vast mycelium and receiving subsidies until they could build enough needles and roots to make it on their own.

The seedlings in this forest were regenerating in the network of the old trees.

A belowground network could explain why seedlings could survive for years, even decades, in the shadows. These old-growth forests were able to self-regenerate because the parents helped the young get on their own two feet. Eventually, the young ones would take over the tree line and reach out to others requiring a boost.

BlackBerry. Nelson was still another 476 kilometers away, and to be home

This forest was like the Internet too—the World Wide Web. But instead of computers linked by wires or radio waves, these trees were connected by mycorrhizal fungi. The forest seemed like a system of centers and satellites, where the old trees were the biggest communication hubs and the smaller ones the less-busy nodes, with messages transmitting back and forth through the fungal links.

These native grasslands were under pressure from exotic weed invasions, and in this case, the mycorrhizal networks were sapping them of life. Knapweeds, spread by cattle, tapped into the mycorrhizas of the grass tillers and stole phosphorus right out of their roots. Instead of the fungi of knapweed helping the grasses thrive, as they had with birch and fir, they were accelerating the decline that had begun with humans herding cattle.

This made sense! Here on the crest, the trees invested more in mycorrhizal fungi because they needed more from them in return. I leaned against the oldest tree, at least twenty-five meters tall with branches like the ribs of a whale. Seedlings were germinating in a crescent along the northern dripline of the tree, their needles stretched like spider legs, and I excavated one with my knife. Fungal threads streamed off the end of its roots, and I felt intoxicated, already forgetting the wasp sting. I pressed the seedling and its woolen mycorrhizas between the pages of my notebook so I could look more closely at home. But I already knew; these little seedlings were linked into the network of the old trees, receiving enough water to get them through the driest days of summer. My students and I had already learned that the deep-rooted trees brought water up to the soil surface at night by hydraulic lift and shared it with shallow-rooted plants, helping the archipelago stay whole during prolonged drought. Without such an attachment, death of a seedling in the hot August days can be nearly immediate, needles turning red and the collars of their stems wounded with burns, leaving not a trace by snowfall. For these young recruits, small resource gains in moments of vulnerability make the difference

between life and death, two sides of the dealer’s card. But once their roots and mycorrhizas reach the labyrinth of russet pores, where water clings in films to soil particles, they ratchet up their game and grow a foundation. A root system like that, unfettered in its opportunity, was far more resilient than the chunky pistons grown in Styrofoam tubes in the nursery, where the seedlings intended for plantations were so stuffed with water and nutrients they couldn’t—didn’t need to—sprout adequate roots to partner with fungi to connect with the soil. Their thick needles needed streams of water under the hot August sun, but their roots continued to grow as though imprisoned, unable to reach the old trees for help when the soil cracked in the dry clear-cuts.

These seedlings were alive, I figured, only because the fungi were importing water from somewhere.

The old trees were the mothers of the forest. The hubs were Mother Trees.

Well, mother and father trees, since each Douglas-fir tree has male pollen cones and female seed cones. But … it felt like mothering to me. With the elders tending to the young. Yes, that’s it. Mother Trees. Mother Trees connect the forest.

This Mother Tree was the central hub that the saplings and seedlings nested around, with threads of different fungal species, of different colors and weights, linking th...

pulled out a pencil and notebook. I made a map: Mother Trees, saplings, seedlings. Lines sketched between them. Emerging from my drawing was a pattern like a neural network, like the neurons in our brains, with some nodes more highly linked than others. Holy smokes. If the mycorrhizal network is a facsimile of a neural network, the molecules moving among trees were like neurotransmitters. The signals between the trees could be as sharp as the electrochemical impulses between neurons, the brain chemistry that allows us to think and communicate. Is it possible that the trees are as perceptive of their neighbors as we are of our own thoughts and moods? Even more, are the social interactions between trees as influential on their shared reality ...

Signaling as precisely as the neurons in our brains do, to make sense of the world. I scribbled quick calculations based on our isotope work. It occurred to me that the amount of carbon transferred relative to nitrogen was strikingly similar to their respective quantities in molecules of an amino acid called glutamate. We hadn’t exactly sought in our experiments to trace glutamate’s carbon-nitrogen movements, but other researchers had verified that the amino acid itself did move through mycorrhizal networks. I

Glutamate was the most abundant neurotransmitter in the human brain, and it set the stage for other neurotransmitters to develop. It was even more abundant than serotonin, whose carbon-to-nitrogen ratio was only slightly greater.

How similar could the mycorrhizal network really be to a neural network? Sure, the pattern of the network and the molecules transmitting from node to node through the links might be similar. But what about the existence of the synapse; isn’t that crucial to signaling in a neural network? This could also be important in a tree detecting whether its neighbors were stressed or healthy. Just as neurotransmitters pass signals across the synaptic cleft from one neuron to another in our brains, signals might also diffuse across a synapse between interfacing fungal and plant membranes in a mycorrhiza.

Could information be transmitted across synapses in mycorrhizal networks, the same way it happens in our brains? Amino acids, water, hormones, defense signals, allelochemicals (poisons), and other metabolites were already known to cross the synapse between the fungal and plant membranes. Any molecules arriving by way of the mycorrhizal network from another tree might also be transmitted through the synapse.

Maybe I was onto something: both neural networks and mycorrhizal networks transmit informatio...

Molecules move not just through the cross walls of adjacent plant cells and the end pores of back-to-back fungal cells, but also across synapses at the apices of different plant roots, or different mycorrhizas. Chemicals are released into these synapses, and the information must then be transported along an electrochemical source-sink gradient from fungal-root tip to fungal-root tip, similar to the workings of a nervous system. The s...

Giving us that flash of brilliance when we solve a problem, or make an important decision, or align our relationships. Maybe from both networks emerg...

It was already accepted widely that plants use their neural-like physiology to perceive their environment. Their leaves, stems, and roots sense and comprehend their surroundings, then alter their physiology—their growth, ability to forage for nutrients, photosynthetic rates, and closure rates of stomata for saving water. The fung...

The mycorrhizal networks could have the signature of intelligence.

The thick complex strands running out from the Mother Trees must be capable of efficient, high-volume transfer to the regenerating seedlings. The finer spreading mycelia must help the new germinants modify to accommodate pressing, rapid needs, such as how to find a new pool of water on a particularly hot day. Pulsing, active, adaptive in providing for the growing plants, like fluid intelligence. The new grant would

eventually show us that the complex mycorrhizal network unraveled into chaos with clear-cutting. With the Mother Trees gone, a forest would lose its gravitas. But within a few years, as seedlings grew into saplings, the new forest would slowly reorganize into another network. Without the pull of the Mother Trees, though, the new forest network might never be the same. Especially with widespread clear-cutting and climate change. The carbon in the trees, and the other half in the soil and mycelium and roots, might vaporize into thin air. Compounding climate change. Then what? Wasn’t this the most important question of our lives? I reached a colossal tree, a rampart, her branches thick right to the ground

“New Policies Needed to Save Our Forests.” We highlighted the sea of clear-cuts, citing how they were “reducing landscape complexity and affecting broad-scale ecological processes such as hydrology, carbon fluxes, and species migrations.” We wrote about young, simplified forests planted solely with single species that were declining due to insect, disease, and abiotic damage, and said this would worsen with climate change. Deep cuts to funding forest science had greatly reduced British Columbia’s capacity to assess the true state of our forests and respond appropriately.

I’d read a paper by Dr. Susan Dudley of McMaster University in Canada about her discovery that an annual plant—the searocket, Cakile edentula, of the Great Lakes’ sand dunes—could distinguish between neighbors that were kin (siblings from the same mother) and those that were strangers, from different mothers, and that the cues came through their roots. Winding my car around the cliffs in the

Birch and fir transmitted carbon to each other, even though they were different species, and to the cedars in their unique arbuscular mycorrhizal network. These old trees were not only favoring their kin, they were also ensuring the community in which they

Mother Trees give their kids a head start, but they also tend the village to ensure it flourishes for their young.

Kin appeared more dependent on Mother Trees in the dry rather than the wet climatic areas. The Mother Tree had especially stepped in to help at the driest site, perhaps by transporting water to her seedlings through the network.

Maybe society should keep old Mother Trees around—instead of cutting most of them down—so they can naturally shed their seed and nurture their own seedlings. Maybe clear-cutting the old, even if they’re not well, wasn’t such a good idea. The dying still have much to give. We already knew the elders were habitat for old-growth-dependent birds and mammals and fungi. That old trees stored far more carbon than young ones. They protected the prodigious amounts hidden in the soil, and they were the sources of fresh water and clean air. Those old souls have been through great changes, and this affected their genes.

Through the changes, they’d gathered crucial wisdom, and they offered this up to their offspring—providing protection, laps into which the new generations got started, the foundation from which to grow.

Were the old Douglas-fir Mother Trees that were unhealthy—sick with disease, stressed from the drought of climate change, or just ready to pass on—using their last moments to transfer their remaining energy and substance to their offspring? With so many forests dying, we should figure out if the elders leave a legacy.

Yuan Yuan and I had already seen that stressed firs passed more carbon to neighboring pines than did healthy firs, and Amanda had also discovered that, in the proximity of healthy Mother-Tree seedlings, kin seedlings had better nutrition than strangers, and their mycorrhizal fungi received more carbon. But so far we hadn’t seen whether dying Mother Trees passed their carbon legacy into the shoots, the lifeblood, of her kin seedlings, beyond the fungal web.

Therefore we couldn’t verify that the carbon transferring into the fungi actually improved the kin seedlings’ fitness. We didn’t know if the fungus kept the carbon for itself, like a middleman, or if the carbon sent by the Mother...

And if the urgency of death compelled a Mother Tree to funnel even more of her substance into the photosynthetic machinery of her children, that would have implications for the entire ecosystem...

Paclitaxel is derived from the cambium of the yew—a short, shrubby tree that grows under old cedars and maples and firs. The Aboriginal people knew its potency, making infusions and poultices to treat illness, rubbing its needles on their skin for strength, bathing in preparations to cleanse their bodies. They used this tree to make bowls and combs and snowshoes, and to craft hooks and spears and arrows. When the anticancer qualities of the yew were brought to the attention of the modern pharmaceutical industry, there was a bounty on the trees. I’d find the small yews—their branches as long as their stems—stripped naked of their bark, looking like crosses, specters of maltreatment.

Our modern societies have made the assumption that trees don’t have the same capacities as humans. They don’t have nurturing instincts. They don’t cure one another, don’t administer care. But now we know Mother Trees can truly nurture their offspring. Douglas firs, it turns out, recognize their kin and distinguish them from other families and different species. They communicate and send carbon, the building block of life, not just to the mycorrhizas of their kin but to other members of the community. To help keep it whole. They appear to relate to their offspring as do mothers passing their best recipes to their daughters. Conveying their life energy, their wisdom, to carry life forward. The yews too were in this web, in relationship with their lifelong companions, and with people like me recovering from illness or just walking through their groves.

The tall waking cedars would be starting to infuse the sleepy little yews with sugars, which would use the energy to grow their shaggy bark and make drops of paclitaxel. As the maple leaves opened, they’d send sugary water to the cedars and yews in the shadows, helping them get enough to drink on the dry summer days. The yews might return the favors to the maples and cedars in late fall, sending sugary reserves from their green cells to help the neighbors slumber through the winter. Mycorrhizal fungi would begin to wrap around the mineral grains, waking up the mites and nematodes and bacteria.

The nagging question remained about the Mother Trees departing from the living. Would ailing mothers send their remaining carbon to their kin—a surge of delivering all she had—and would it move beyond the webbing of fungi enveloping their tiny roots and into their nascent leaves, helping them grow their budding photosynthetic tissues? Her last breath entering—becoming part of—her progeny.

we discovered that the birch trees whose roots ran freely and connected with the firs were almost twice the size of those in the trenched plots, and they were free of disease. Compared to the birches we’d thinned alongside the creek nearby two decades ago, these were smaller, but they were healthy, the papery bark thick, lenticels (eyelets) compact, branches few, valuable for making baskets.

Mary Thomas’s grandmother Macrit showed her how to peel the bark so as not to hurt the tree, as her grandmother had shown her, and as Mary would show her own grandchildren. Teaching them how to leave the pulpy cambium intact so it would be primed to heal over, to ensure the tree seeded new generations. They used the bark to make baskets of all sizes, some for thimbleberries, cranberries, and strawberries. The impermeable bark of the bigger birches down by the river would be perfect for canoes, the luxuriant leaves for soap and shampoo, the sap for tonics and medicines, the best wood for bowls and toboggans. With care—planted in rich soil, with good neighbors, in proper numbers, and with roots unrestrained—even these upland birches could become prominent providers in the forest. Woven among the birches, the firs were also a little bigger than where we’d trenched between them, and they were in prime condition. In the early years, the mycorrhizal connections with birch had helped the fir saplings grow taller, and in adulthood, this head start still mattered. Two decades later, firs performed better in the neighborhood of birches than where they’d been cut off from their neighbors or where they’d grown only among other firs.

They had better nutrition—the rich birch leaves building the soil—and less Armillaria root disease, the bacteria along the birch roots providing a bundle of nitrogen and immunity with a potent mix of antibiotics and other inhibitory compounds. Grown intimately together, this forest had almost twice the productivity of the stands where we’d trenched between the species two decades earlier.

This was the opposite of the usual foresters’ expectations. They figured that fir roots free of birch interference would obtain more of the resource pie, as though the ecosystem worked as a zero-sum game—the adamant belief that greater total productivity cannot possibly emerge from species interactions. Even more surprising to me was that birch benefited from fir too. Not only did birches likewise grow at twice the rate when intimately connected with firs than when alone, but they also had fewer root infections. The birches that had delivered food and good health to the firs when they were young were now being helped in reciprocity by the bigger firs as adults. Although the birches were retreating as the firs grew skyward, as happens naturally with the aging of these forests, their roots were still deep in the soil, their legacy of fungi and bacteria intact, lifeblood painted ...

“Why are the plants so sweet under the birches, Auntie Suzie?” she asked. Their roots and fungi draw water from deep in the soil, I told her, and with it bring calcium, magnesium, and other minerals, and this feeds the leaves so they can make sugars. The birches, with their cables of fungi, knit the other trees and plants together, and through their web share the nutritious soup drawn from the soil and also the sugars and proteins made by their leaves. “In the fall, when the birch leaves drop, they nourish the soil in return,” I said. Mary

Mary’s people had known this of the birches for thousands of years, from living in the forest—their precious home—and learning from all living things, respecting them as equal partners. The word “equal” is where Western philosophy stumbles. It maintains that we are superior, having dominion over all that is nature.

“Remember how I said the birches and firs talk to each other underground through a fungal web?” I asked the girls, putting my hand to my ear and my finger to my lips. The girls listened, their ears filled with mosquito songs. I told them I wasn’t the first person to figure this out, that this was also the ancient wisdom of many Aboriginal people.

I’d been taught in the university to take apart the ecosystem, to reduce it into its parts, to study the trees and plants and soils in isolation, so that I could look at the forest objectively. This dissection, this control and categorization and cauterization, were supposed to bring clarity, credibility, and validation to any findings. When I followed these steps of taking the system apart to look at the pieces, I was able to publish my results, and I soon learned that it was almost impossible for a study of the diversity and connectivity of a whole ecosystem to get into print. There’s no control! the reviewers cried at my early papers.

Somehow with my Latin squares and factorial designs, my isotopes and mass spectrometers and scintillation counters, and my training to consider only sharp lines of statistically significant differences, I have come full circle to stumble onto some of the indigenous ideals: Diversity matters. And everything in the universe is connected—between the forests and prairies, the land and the water, the sky and the soil, the spirits and the living, the people and all other creatures. We walked in the drizzle to where I’d planted conifers at different densities, to see how they liked growing in pure stands with few neighbors, or many. I knew every tree, every plot, every corner post. I knew where the larch was planted and the cedar. The fir and the birch. I showed the girls how this fir was planted too deep, that birch had been broken by a moose, this larch got pushed sideways by a black bear. I’d planted another spot every year for five years, but a tree would never take, and now it was a beautiful patch of lilies, what it was meant to be. In the mixed plots, cedars were luxuriant under birches, needing their cover to protect the pigments in their delicate leaves. When I stopped chattering and looked up, Jean and the girls were grinning.

We settled into measuring the Douglas firs planted at different densities. Without birch neighbors, up to 20 percent had become infected by Armillaria disease, more where the firs were tightly clustered. Their roots had grown into infection pockets in the soil, and the pathogens had spread under their bark, strangling the phloem, no birch roots to stop them. Some of the infected firs were still alive—needles yellowing—and others were long dead, their bark gray and flaking. In their place, other plants grew, and even some birches had seeded in, inviting the warblers and bears and squirrels. Some mortality wasn’t a bad thing. It made room for diversity, regeneration...